Is there a way to mimic the 'inherit rotation' of a bone?
I'm assuming this is an IK chain, because if not the foot will always follow the knee rotation. In IK chains generally this behaviour is obtained by making the knee pole target child of the foot, so that you rotate the foot and the knee rot follows (while you're trying to do the inverse).
If you really need this inversion you can create a bone in the loc of the knee with the same orientation of the foot bone; make it child of the knee bone; set a copy rot constraints on the foot bone following only the rot axis needed (in my example Z axis).